180 ODOROGRAPHIA. 
To free the crude oil of bitter almonds from hydrocyanic acid, 
the following methods have been adopted :— 
1. (Liebig.) Agitate the crude distilled oil with red oxide of 
mercury in slight excess, and after a few days’ contact rectify the 
oil from a little fresh oxide of mercury. The product is quite 
pure when the process is properly managed. The cyanide of 
mercury thus formed may be either employed as such or re- 
converted into mercury. 
2. (Mackay.) Crude oil of almonds | Ib. ; fresh slaked lime gq. s. 
to form a milk-like liquid; afterwards add 14 lb. solution of 
potash and 3 pints of water; agitate occasionally for 48 hours, 
then distil over the oil and rectify it from a fresh mixture of lime 
and potash. 
3. (Redwood.) The oil is mixed with an equal quantity of 
water, and the mixture is digested in a water-bath with red oxide 
of mercury and small quantities of fresh slaked lime and proto- 
chloride of iron, with as little access of air as possible; as soon 
as the decomposition of the acid has taken place the whole is 
introduced into a copper retort and submitted to distillation. 
The product is perfectly free from hydrocyanic acid. 
The first process is considered the simplest, cheapest, and best. 
The usual method of testing Bitter-almond oil for prussic acid is 
given in the description of Artificial Benzaldehyde, further on. 
Artificial Oil of Bitter Almonds. 
Benzaldehyde is manufactured artificially on the large scale by 
boiling 2 parts of Benzyl chloride with 3 parts of lead nitrate 
(or, preferably, copper nitrate) and 10 parts of water for several 
hours in an apparatus connected with an inverted condenser, the 
operation being conducted in a current of carbon dioxide; half 
the liquid is then distilled off, and the oil separated from the 
water. 
It is obtained from benzidene chloride by heating it under 
pressure in an iron vessel with caustic soda. It is said to be 
possible to heat without pressure in an apparatus connected with 
an inverted condenser if milk of lime be used, or if whiting or 
some other finely divided insoluble substance be added and the 
whole stirred into an emulsion, which boils at a higher temperature 
and thus facilitates the decomposition of the chloride. 
